How delineate sub-basins for urban storm drain network?

I am struggling to find a way to delineate sub-basins for an urban storm drain network, with raster terrain and vector outlet points (hundreds of storm drain inlets). I had hoped to burn in the storm drain inlet locations with lower elevations in the terrain, to force sinks at those locations, then I could just delineate basins using small stream definitions, then aggregate the mini-sub-basins together. This would be a bit of work, but I can't even get this to work, as when I take the inlets point shapefile (with a "-10" value for all records in the elevation field) and create a raster, it only creates at the discrete inlet location points, and when I add it to the basin terrain raster, it only outputs the revised elevations at the inlet locations, as it seems that every raster math I have tried will not create a value if there is NoData at one of the input rasters.

Ideally, there would be a way to create a basin with multiple outlet points (I need about 150 for my current model), but it appears that neither ArcHydro or GeoHMS have the ability to work with more than 1 outlet. Trying to generate the sub-basins individually would be a nightmare, as you would have to start at the uppermost inlet, then to the next downstream inlet and manually remove the area of all upstream inlet capture areas, and repeat until all areas had been identified. Unless some automated way is available, I will end up just manually delineating the areas by following contours, as has been done for ages.

I have use ArcHydro/GeoHMS for delineation of surface hydrology (i.e. without stormdrain inlets and underground conveyance) for 20 years, and that's a piece of cake, but I have been beating my head against a wall trying to solve the urban drainage problem. If somebody knows of a helpful tool, I would appreciate learning about it. If there is not one yet, it does not seem like it would be a difficult exercise for one to be created by a person with some GIS coding skills (perhaps I can get one of David Maidment's students to do this).

Your drainage inlet points currently are just that, you need a network to produce water movement using those. As for water crossing roads from one side to the other, you need to have a vector connecting the pooints. When this is converted to a raster, the elevation difference should be negative as you indicate, however the surrfounding area must be converted from nodata to zero, so that when you "add" that layer to the DEM for burning in, a depressive elevation is there and water is able to traverse an otherwise block. This problem is going to more pronounced the more representative of the actual terrain your dem is.

Did you ever find a viable solution for this workflow? I am about to start a similar initiative, so I am interested in what you've been able to develop. My intent was similar in that I will need to delineate storm sewersheds, but I also need to provide spill response support to EMS/utilities so am thinking the storm drain system will need to be a geometric network in order to do a network trace, next downstream inlet, etc., and then serve it as a geoprocessing service. Any insights from your experience would be helpful. Cheers.

I have added under Featured Contents a draft document describing how Arc Hydro may be used to process the raster and vector data to support stormwater delineation. This is a draft but it will show you the workflow as well as the new tools created to support it. Basically we burn in the inlets so that they act as sinks collecting the water and transmitting it to the stormwater system. Each inlet has an associated sinkwatershed which is the contribution to the inlet. The pipes and natural streams are connected with the inlets using a geometric network so the water may be traced upstream through the pipes and streams, and associated to the sink watersheds associated to the upstream inlets.